Fix Style/ReductantReturn rubocop

Exclusions from .rubocop_todo.yml deleted.This cop checks for redundant return expressions.
Fixes #1824

app/helpers/application_helper.rb

@@ -66,7 +66,7 @@ module ApplicationHelper
     else
       ts = all.join
     end
-    return ts
+    ts
   end
 
   def difficulty_levels(conference)
@@ -80,7 +80,7 @@ module ApplicationHelper
     else
       ts = all.join
     end
-    return ts
+    ts
   end
 
   def unread_notifications(user)

app/helpers/format_helper.rb

@@ -101,17 +101,17 @@ module FormatHelper
 
   def icon_for_todo(bool)
     if bool
-      return 'fa fa-check'
+      'fa fa-check'
     else
-      return 'fa fa-times'
+      'fa fa-times'
     end
   end
 
   def class_for_todo(bool)
     if bool
-      return 'todolist-ok'
+      'todolist-ok'
     else
-      return 'todolist-missing'
+      'todolist-missing'
     end
   end
 

app/helpers/paths_helper.rb

@@ -5,9 +5,9 @@ module PathsHelper
 
   def active_nav_li(link)
     if current_page?(link)
-      return 'active'
+      'active'
     else
-      return ''
+      ''
     end
   end
 end

app/helpers/users_helper.rb

@@ -18,7 +18,7 @@ module UsersHelper
       providers << provider if !ENV["OSEM_#{provider.upcase}_KEY"].blank? && !ENV["OSEM_#{provider.upcase}_SECRET"].blank?
     end
 
-    return providers.uniq
+    providers.uniq
   end
 
   # Receives a hash, generated from User model, function get_roles